1. Field of the Invention
The invention relates to an apparatus which allows adjustment of the air flow rate through a fan without adjusting the rpm of the fan blades. More specifically, the invention relates to an apparatus which adjusts the amount of fan blade which can effectively move air through the fan.
2. Brief Description of the Prior Art
Prior to the present invention, when it was required to regulate the flow of air through a fan, the common mode of regulation was to adjust the rpm of the fan blades. This was accomplished by changing the speed of the drive motor, or by using a transmission system which allowed the motor speed to remain relatively constant while changing the speed of the drive shaft. Both prior art methods of air flow adjustment required extensive modifications and/or additional machinery attached to the drive motor.
Others have attempted to solve the problem of adjusting the air flow rate through a fan without resorting to a change in rpm of the fan blades but have not had much success. Generally, the prior art approach has been to move the fan blades or the entire fan in some cases ( i.e., blades, shaft, and even the drive motor), into and out of operating relationship with an air exit vent. For example, Youker, U.S. Pat. No. 2,100,152, discloses a vent fan mounted on guide rods and movable thereon along a horizontal axis to adjust the location of the fan blades in the vent path, and also the size of the exit vent itself. McLarty, U.S. Pat. No. 2,837,021, also shows a fan mounted on a rod for horizontal movement in and out of an air vent. Lange, U.S. Pat. No. 1,467,901, and Parrott et al., U.S. Pat. No. 1,529,711, disclose ventilator fan arrangements which include fan blades which are adjustable along the length of their axis. In each of the above cases, the apparatus required to move the fan in relation to the exit vent, is complicated and extensive. Also there is no adaptability of the prior art devices for use with very large or heavy fans. As can be seen in the prior art devices, moving the entire fan in and out of an exit vent becomes very impractical with fans of large size or significant weight.